A Narrative Review of the Role of Adjuvants in Adult RSV Vaccines

The development of respiratory syncytial virus (RSV) vaccines has advanced substantially in recent years, with three prefusion F (preF) protein-based and mRNA platforms achieving regulatory approval for use in older adults. Among licensed protein subunit vaccines, key design differences include the use of adjuvants and antigen valency, raising important questions regarding the necessity and impact of adjuvantation for RSV prevention. This narrative review examines the role of adjuvants in RSV vaccine development, with a focus on immunogenicity, vaccine effectiveness, safety, and implications for older adults and immunocompromised (IC) populations. Adjuvants can sometimes enhance immune responses but may increase reactogenicity. Clinical trials and observational studies demonstrate that both adjuvanted (RSVPreF3/AS01E) and non-adjuvanted (bivalent RSVpreF) vaccines provide substantial and comparable protection against RSV-related lower respiratory tract disease and hospitalization with comparable safety. The totality of evidence to date does not suggest an effectiveness advantage for adjuvanted vaccines among IC populations. Overall, these findings suggest that effective protection against RSV disease in adults can be achieved with or without adjuvantation.